bbb_cape/src/bbb/gpios.cc

#include <cstdio>
#include <cstdlib>

#include "aos/common/logging/logging_impl.h"
#include "gpios.h"

namespace bbb {

  Pin::Pin(int bank, int pin) : handle_(NULL), direction_(0),
    kernel_pin_(bank * 32 + pin), exported_(false) {}

  Pin::~Pin() {
    // Unexport the pin.
    if ((handle_ = fopen("/sys/class/gpio/unexport", "ab")) == NULL) {
      LOG(WARNING, "Could not unexport gpio pin.\n");
      // There's nothing intelligent we can really do here.
      return;
    }

    char gpio_num[2];
    snprintf(gpio_num, sizeof(gpio_num), "%d", kernel_pin_);
    fwrite(gpio_num, sizeof(char), 2, handle_);
    fclose(handle_);
  }

  int Pin::DoExport() {
    char gpio_num[2];
    snprintf(gpio_num, sizeof(gpio_num), "%d", kernel_pin_);
    
    // Export the pin.
    if ((handle_ = fopen("/sys/class/gpio/export", "ab")) == NULL) {
      LOG(ERROR, "Could not export GPIO pin.\n");
      return -1;
    }

    fwrite(gpio_num, sizeof(char), 2, handle_);
    fclose(handle_);

    exported_ = true;
    return 0;
  }

  int Pin::DoPinDirSet(int direction) {
    char buf[4], type_path[64];
    snprintf(type_path, sizeof(type_path), "/sys/class/gpio/gpio%d/direction", kernel_pin_);
    
    if ((handle_ = fopen(type_path, "rb+")) == NULL) {
      LOG(ERROR, "Unable to set pin direction.\n");
      return -1;
    }

    direction_ = direction;
    switch (direction) {
      case 1:
        strcpy(buf, "in");
        break;
      case 2:
        strcpy(buf, "low");
        break;
      case 0:
        return 0;
      default:
        LOG(ERROR, "Invalid direction identifier %d.\n", direction);
        direction_ = 0;
        return -1;
    }
    fwrite(buf, sizeof(char), 3, handle_);
    fclose(handle_);

    return 0;
  }

  int Pin::MakeInput() {
    if (!exported_) {
      if (DoExport()) {
        return -1;
      }
    }

    return DoPinDirSet(1);
  }

  int Pin::MakeOutput() {
    if (!exported_) {
      if (DoExport()) {
        return -1;
      }
    }

    return DoPinDirSet(2);
  }

  int Pin::Write(uint8_t value) {
    if (direction_ != 2) {
      LOG(ERROR, "Only pins set as output can be written to.\n");
      return -1;
    }

    char buf, val_path [64];
    snprintf(val_path, sizeof(val_path), "/sys/class/gpio/gpio%d/value", kernel_pin_);
    if (value != 0) {
      value = 1;
    }

    if ((handle_ = fopen(val_path, "rb+")) == NULL) {
      LOG(ERROR, "Unable to set pin value.\n");
      return -1;
    }

    snprintf(&buf, sizeof(buf), "%d", value);
    fwrite(&buf, sizeof(char), 1, handle_);
    fclose(handle_);

    return 0;
  }

  int Pin::Read() {
    // NOTE: I can't find any docs confirming that one can indeed
    // poll a pin's value using this method, but it seems that it
    // should work. Really, the "right" (interrupt driven) way to
    // do this is to set an event, but that involves messing with
    // dev tree crap, which I'm not willing to do unless we need 
    // this functionality.

    if (direction_ != 1) {
      LOG(ERROR, "Only pins set as input can be read from.\n");
      return -1;
    }

    char buf, val_path [64];
    snprintf(val_path, sizeof(val_path), "/sys/class/gpio/gpio%d/value", kernel_pin_);

    if ((handle_ = fopen(val_path, "rb")) == NULL) {
      LOG(ERROR, "Unable to read pin value.\n");
      return -1;
    }

    if (fread(&buf, sizeof(char), 1, handle_) <= 0) {
      LOG(ERROR, "Failed to read pin value from file.\n");
      return -1;
    }
    fclose(handle_);
    return atoi(&buf);
  }

} // bbb